Selective time-limit-controlling device for electric switches.



G. A. BURNHAM.

SELEGTIVE TIME LIMIT GONTRDLLING DEVICE FOR ELEGTRIG SWITCHES.

APPLICATION FILED JULY 17,1911.

G. A. BURNHAM. SELECTIVE 'TIME LIMIT CONTROLLING DEVICE POR ELECTRIC SWITCHES. APPLICATION PILEI) JULY 17,1911. 1,041,71 6. l Patented oct. 15, 1912.

6 SHEETS-SHEET 2.

G. A. BURNHAM.

SELEGTIVE TIME LIMIT GONTROLLING DEVICE FOR ELECTRIC SWITCHES.

APPLICATION FILED JULY 1v, 1911.

1,041,7'1 6. Patented oct. 15, 1912.

G. A. BURNHAM.

SELEOTIVE TIME LIMIT GONTROLLING DEVICE FOR ELECTRIC SWITCHES.

APPLICATION FILED JULY 17,1911.

1,041,716. Patented 0111.111912.

6 SHEETS-SHEET 4.

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0 v` m1116556@ SCNOQBQ Inaentor' G. A. BURNHAM. Y

SELECTIVE TIME LIMIT CONTROLLING- DEVICE FOR ELECTRIC SWITCHES. APPLICATION FILED JULY 17,1911.

1,041,716. Patented 001.15, 1912.

6 SHEETS-SHEET 5.

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G. A. BURNHAM.

SELECTIVE TIME LIMIT CONTROLLING DEVICE FOR ELECTRIC SWITCHES.

APPLICATION FILED JULY 17,1911.

1,041,716. Patented 0@1;.15,1912.

6 SHEETS-SHEET 6.

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Wl ness es Ina@ n tor ff 03. Q, @TAL/QQ A f/Mlfu., afa@ UNITED sTATEs PATENT oEEioE.

GEORGE A. BURNHAM, OF SAUGUS, MASSACHUSETTS, ASSIGNOR To s. B. OONDIT, JR.,

OF BOSTON, MASSACHUSETTS.

SELECTIVE TIME-LIMIT-CONTROLLING DEVICE FOR ELECTRIC SWITCHES;

Specification of Letters Patent.

Patented Oct. 15,1912.

Application led July 17, 1911. Serial No. 638,846.

Massachusetts, have invented an Improve-I ment in Select-ive Timel-Limit-Controlling Devices for Electric Switches, of which thefollowing is a specification.

This invention relates to time-limit controlling-devices for electric-switches. -Heretofore time-limit controlling-devices for f .electric-switches have been devised requiringfa prolonged period of time to operate the switch, the speed of which was constant regardlessof the strength of the overload; ,also tlme-llmit controlling-devices have been devised requiring a prolonged period of time to operate the switch, the speed of which was variable, depending upon the strength of the overload. In the first-named instance, in case an overload greatly exceeds the normal setting of the controlling-device said device will not Operate quickly enough to protect the apparatus; and in the last named inst-ance, in case the overload is excessive the controlling-device will operate almost instantly, re.- gardless of its setting. In case several controlling-devices of the last named type are connect-ed in a circuit, and arranged with different se'ttings, so as to operate selectively on a given overload, they will all operate almost instantly and practically' simultaneously upon an excessive overload, hence they will not be selective, and as a result some of the circuits will be opened unnecessarily, which is very objectionable.

`One of the objects of this invention is the construction of a time-limit controlling-device for electric-switches adapted to be operated by an overload current, and when used in connection with other/like controlling-devices, all will be selective, regardless of the strength of the overlo-ad, the object being particularly to produce a device which will be selective on a heavy overload, as for instance, an overload in excess of approximately three times the full load of the circuit Which is controlled by the switch.

The .time-limit controlling-device embodying this invention comprises a movable element to con-trol the operating-means for the switch, a coil for said movable element having its magnetic-circuit and windings so A 'proportioned that upon the occurrence of a light overload, as for instance an overload less than three times the full load of the circuit controlled by ,the switch, or thereabout,

the force which is exerted by the movable element is variable according to the Strength 4of the overload, or, in other words, is proportionate to the overload, and upon the occurrence of a heavy overload, as for instance an overload which is three or more times the fullJ load of the circuit, the forcewhich is exerted by the movable element is constant regardless of the strength of the overload. The operating-means for the switch is constructed and arranged to require a prolonged period of time to operate the switch, L

and means are provided for adjusting said operating-means whereby said period of time may be varied so that the device may be used in connection with other like devices, and all of the devices adjusted differently. For a light overload the devices can be made to operate selectively by an adjustment ofthe operating-means. In such case the movable elements of all the devices will be operated at a speed corresponding or proportionate to the strength or current value of the overload, and by reason of the different adjustments, will cause the operating-means which is set to operate: on the shortest period of time to operate the switch at the end of such period of time. Such period of time, however, is variable according to the strength or current value of the.

overload. For a heavy overload adjustment of the operating-means alone is not suiicient to enable the devices to operate selectively, but by constructing and arranging :the movable element and coil in accordance ing the switch operating-device at a variable speed according to the strength of the overload current up to the point of Saturation, hereinafter referred to and at a. definite or constant speed on overloads of higher current values.

1t also involves 'means controlled by the overload current for moving the operating- `device into engagement with its actuator,

which permits movement thereof out of engagement when the overload ceases, said means also driving said actuator; and in so far as t-his feature is concerned, the invention also involves an electric-motor which may or may not have the characteristics above set forth, which is constructed and arranged to rotate the actuator for the switch operating-device, and also tov effect engagement of said switch-operating-device with its actuator and permit disengagement therefrom.

1talso involves means for retarding the speed of movement of the motor whereby it may be more eectively controlled during the prolonged period of time which it consumes in operating the switch.

ltt also involves means connected with the motor for controlling the starting thereof, whereby it will beheld at rest on an overload current of lesser value than that which is designed to start and operate it, such provision enabling the usual overload relay which controls the transformer-circuit to be omitted.

Figure 1 is a side elevation of a timeactuator, the parts being. disengaged, and in.

their normal positions. Fig. l is a detail of the o-perating-device and actuator, the parts being in engagement. Fig. 5 is a vertical section of the device shown in Fig. 1, taken on the dotted line 5 5. Fig. 6 is adetail of electric means for retarding the speed of the motor. Fig. 7 is another modication to be referred to. Fig. 8 is adiao-rammatical view of the circuits which may he employed in connection with the timelimit controlling-device, to illustrate the operation of the same. Fig. 9 is a detail View illustrating particularly a modified form of operating-means for the switch. Fig. 10 is a detail view illustrating particularly the switch adapted to be operated directly by the. timed operating-device. Fig. 11 is a view of a chart, illustrating by chart lines vthe operation of the time-limit controllingdevice. Fig. 12 is a diagramA of a transformer circuit and time-limit controllingdevice for the switch, wherein the voverload relay is omitted. I Figs. 13 to 18 inclusive are modied forms of means responsive to an overload current to actuate the operating means for the switch.

Referring to Fig. 8, wherein a single linecircuit isshown, as a simple manner of illus- 4trating my invention, 20 represents a circuit or line-wire, and 21 a switch included there- 1n, which may be of any suitable construcmamie tion, but preferably of a type adapted to l be operated automatically to open the c1rcuit and manually to close the circuit. A snap-switch of usual construction is here shown, having a hand-lever 22 and an actuating-spring 23. This is the switch which the time-limit controlling-device, forming the subject-matter of this application, is designed to operate automatically, for the purpose of opening the circuit 20. rlhe timeimit controlling-device includes operatingmeans for the switch and means responsive to an overload current to operate said means or to control its operation. Said switch operating-means may comprise aI timed operating-device and a switch-controller which is adapted to be operated by the timed operating-device, although the switch may be operated directly by said timed operating-device. A switch-controller such as may be employed is represented in Fig. 8, which consists of an electro-magnet 24, connected in a battery-circuit 25, controlled by the circuit-closing members 26, 27; and the armature of said magnet is connected to a lever 28, secured to a pivot-shaft, to which 'shaft is secured a short arm 29, designed to engage and operate the snap-switch to open the circuit 2() upon energization of the magnet. 'Fhe circuit-closing members 26, 27, are normally open, and are adapted to be closed by the timed operating-device to close the circuit 25, to operate the switch 21 automatif of illustrating 'one practical form which may be employed. lln lieu thereof a mechanical switch-controller may be employed, such for instance as shown in Fig. 9, wherein a spring-controlled bar 30, is arranged at the side of the lever-mechanism of the switch 2] which upon a longitudinal sliding movement against the force of its controlling or return-spring 31, acts to move said levermechanism to operate the switch and open the circuit 20. Said bar is arranged to move but a short distance in order to operate the lever-mechanism, but during such movement 1t is constantly under the control of the spring 31, so'that when pressure u on it is relieved it will be returned immedlately by said spring, regardless of the distance it has moved. By making said bar independent of the switch and providing it with a controlling-sp-ring of its own, it will be automati-l cally/returned to normal when pressure upon it is relieved.

ln case a mechanical switch-controller, such as shown in Fig. 9'is employed for automatic operation, it is of particular advantage to arrange it in connection with a crate the switch it will be returned to normal automatically, and when said overload current is continued it will cause the switch to operate quickly.

In Fig. l0, the switch 2l is arranged to be operated directly by the timed operatingdevice, its toggle-lever-mechanism having a pin 33, adapted to be engaged by a member of said device. -y

Referring to Figs. l, 2 and 4, wherein the electric switch-controller is shown, the circuit-closing member 2G, is made as a resilient bent strip of metal, secured to the top of a block 35, of insulating material, attached to the field-frame of an electric-motor, (although it may be otherwise supported), and the circuit-closing member 27 is made as a resilient bent strip of metal secured to the under side of said block, its free end being extended to a position beneath the free end of the member 26, to permit of its being lifted into engagement with said irember 26, to close the circuit 25; and the circuit-wires of said circuit 25 are connected respectively to said members at 36, and 37 although it is obvious said circuit-closing members may be otherwise constructed.

The operating-device for the switch-controller or for the switch, as the case may be, is constructed and arranged to be moved to operate the switch-controller or the switch at the end of a prolonged period of time, hence is time-controlled, and as time-controlled operating-devices for circuit-closers are very old in the electrical art anyof the well-known forms may be employed, so far as this invention is concerned; although the particular form here shown involves novel features. is here shown it comprises a yoke or arm 40, arranged to-'be moved rotarily in a vertical plane, having at'its extremity a cross-piece or pin 41 of insulating material, which, when the yoke or arm is moved through an interval of space is adapted to engage the circuit-closing member 27, and move it into engagement with the circuitclosing member 26. Said yoke or arm is mounted loosely on a shaft 42, to which a worm-wheel 43 is secured, and means as a screw 44 is provided for adjust-ably con-- necting said yoke or arm with said wormwheel in different radial positions, said screw entering any one of a series of holes 45, arranged in the side of said Aworm-wheel, so that the yoke or arm will be moved by said worm-wheel. Said worm-wheel also has a pin 46 projecting from its side which or arm is moved by it through a definite interval of space, according to its setting to engage with t-he under circuit-closing` member 27.

Referring to Fig. 9, the sliding bar 30 has its end formed with an inclined portion which is adapted to be engaged by the yoke or arm 40, for the purpose of moving said bar to operate the switch; and referring to Fig. l0, said yoke or arm 40 has an inclined end portion adapted to engage a pin 33 on the toggle lever-mechanism of the switch. Hence said yoke or arm is selected as the meirber of the operating-device which is employed to operate the switch-controller or the switch. The movement of saidwormwheel and yoke or arm to close the ycircuit 25, of the switch, requires a prolonged period of time, and such movement is controlled by means responsive to the overload current, so that the operating-device is'controlled by the overload current. yAs a means to move the worm-wheel and the yoke or arm an electric-motor is employed.

48 represents the armature of the mot-or, which is supported in suitable bearings, and one-end of the shaft of said armature is extended` as at 49 and is threaded to form a worm. The worm-wheel 43 is supported by a movable member beneath said worm and is movable into and out of engagement therewith, but is normally out of engagement. Said worm serves as the means to drive the worm-wheel, and therefore constitutes the actuator of the operating-device'.

The engagement of the operating-device with its `actuator is controlled by the same current which operates the'motor, and, herein the worm-wheel 43 is supported byan extension of the lower part of the field-frame of the motor, which is made movable with respect to the upper part thereof, whereby the worm-wheel is moved into and out of engagement with its actuator. The fieldframe of'the motor is or may be made in two parts, er may have a movable part in connection with it, and, as here shown, said frame is divided on a horizontal line, 50 representing the upper part and 5l the-.lower part; and said parts are hingedly connected together at 52, so that the lower partis movable toward and from the upper part, and

`the upper part `y'is held stationary, being herein connected to a support 53. With the exception of making' the field-frame in two parts it may be constructed, generally speaking, in any well-known or suitable manner to support the field-coils. Movement ofthe lowerpart 5l in a direction away from the upper part is limited by anadjustable yielding stop comprising, as shown in Fig. 1, a pin 55, extended through an ear 56, yarranged thereon, which engages a spring 57, resting against a fixed abutment 58, which maybe a downward extension of the upper part. The lower end of the ear 56 has a hole through it for a bar 60, which is horizontally arranged and secured to the ext-ension 58, and which projects throughI said hole for a considerable distance, and a spring is arranged on said bar between the ear 56 and anut 61, adjustably arranged on the bar, which exerts its pressure upon the ear in a direction to move the lower part of the frame downward. Upward movement of the frame acts to compress said spring, so that such movement is resisted by the spring, and by adjustment of the spring a greater or less force will be required to lift the frame. 'lthe bar 60 may be calibrated, if desired, to indicate in amperes the force required to lift the frame by the magnetic influence due to the current traversing the field-coils of the motor and causing the motor-frame to act as magnet. 'lhus the spring 59, not only acts as a rectractile spring to assist gravity in moving the part 51 away from the part 50, but also may be employed to determine the amount ot energy required to lift it, and in this respect serves as an adjusting-device for the motor, whereby it may be caused to move the operating-device into engagement with its actuator only upon an overload of a given value or in excess oit such value.

When the lower part of the field-trame is in its lowermost position, being removed from or remote from the upper part, as represented in Fig. 5,.i said worm-wheel is removed trom engagement with the worm, and when said lower part of the field-frame is in its uppermost position, as represented in Fig. 1, said worm-wheel is in engagement with the worin.

The motor is or may be-'arranged in a transformer circuit 70, see Fig. 8, in connection with the secondary-coil 71 of a trans-V former, the primary-coil 72 ot said transformer being arranged in the circuit 20, so that the motor is operated by the current from said circuit through the transformer. As represented in Fig. 8 said mot-or is normally short-circuited by a switch or circuitcloser, the Fixed members 7 3 of which are engaged by a plate 74, connected with the armature of a'solenoid 75, which is included in t-he transformer-circuit 70, so as to be energized'by a current from the circuit 20 through the transformer. Said solenoid 75 serves as, and constitutes the overload relay, and is adjusted to be operated by the overload current through the transformer. lit may or may not be employed, and in Fig. l2 it will be observed that the motor is con! nected directly in the transformer circuit, said overload relay being omitted. When the overload relay attracts its armature the circuit-closer 73, 74, will. be operated to open" the short-circuit of the motor so that the motor will be operated by the overload curmamie rent through the transformer; or in case said overload relay is omitted the motor whenv yating-device for the switch-controller will be moved into engagement with its actuator,

, and will be driven by said actuator, and the movable member 40 of the operating-device will be moved rotarily into engagement with the circuit-closing member 27 and will movev said member 27 into engagement ywith the circuit-closing member 26, and thus close the switch-circuit, so that the switch will be operated and the line circuit open, whereupon the current ceases and the motor comes to rest, the lower part of the field-.frame returns to its normal position, the operatingdevice "is moved out of engagement with its actuator, and the movable member 40 of the operating-device is moved out of engagement with the member 27, permitting said member 27 to disengage the member 26, and open the switch-circuit, and as the parts thus assume their normal positions said movable member 40, and worm-wheel to which it is attached will be returned to normal position, moving counter-clockwise by gravity incident toithe weight of the yoke or arm. sv suming. the overload current passes over the circuit for a short period of time and then ceases, and such period oi time is insufhcient to drive the operating-device far enough to cause its yoke or arm 40 to engage the member 27, then, as soon as said overload current ceases, the overload relay will return to normal andall the remaining parts will also return tonormal automatically.

rlhe motor has the general characteristics l of a series motor, whereby the speed of its armature is variable` according 'to the strength or value of the current, and herein such manner that its magnetic circuitand windings are so proportioned that an overload in excess of approximately three times the full load of the circuit will saturate the same to cause the motor-armature to attainl its maximum speed. A light overload, meaning' an overload less than approximately VAthree times the yfull load of the current, will cause the motor-armature to rotateat a slower speed, that is to say, aspeed vsaid motor is constructed and arranged in currents by means of electro-magnetic action, and such a device when constructed and arranged to exert a variable force proportionate to the current value of the overload up to its point of saturation and to eX- ert a. constant or definite force on overloads of higher current values, comes Within the spirit and scope of my invention, but it will be understood that said motor however constructed to accomplish the aforesaid result is employed' in connection with a time element, so that an appreciable length of time is always consumed in operating the switch. This motor or any equivalent form of motor having` the same characteristics, when used to operate switch-operating mechanism arranged to require a prolonged period of time to operate the switch, results in a prolonged period of time being required on all overloads, but the length of said period of time .is variable according to the current value of the overload up to a predeterminedv current value and is constant on all overloads of higher current values. This result yis of the greatest importance for it enables a set of time-limit controlling-devices to be selective regardless ofthe strength of the overload.

By referring to Fig. 11, a representation of a chart is shown having chart-lines which indicate the action of four time-limit controlling-devices having different settings for a tive ampere overload through the transformer. They are set to operate respectively in four andthree tenths, eleven, thirteen and eighteen seconds, and will operate selectively in regular order on the given overload. In case of an excessive overload, say twenty ampere overload, the chartline shows that the first named device will operate in about one-half second, the second in about one second, the third in about one and three-fourths seconds and fourth in about two and two-tenths seconds.

that the inverse curve of each chart-line terminates in a direct or straight line', and the several straight lines of the several devices are in parallel, and will so continue, instead of intersecting, so that their selective action is insured upon the occurrence of any overload.

For the purpose of retarding the speed of the motorshaft to more effectively control the speed of the operating-device-when said device is in engagement with its actuator, and is being operated by the overload, a disk may be secured to the motor-shaft, see Fig. 6, which is composed of copper or equivalent material, and a magnet 8l is arranged adjacent said disk so that the disk moves in the ,field of said magnet to generate a current which dissipates itself in heat and acts to load down the motor. Said electric retarding means may or may not be The y 45 important feature to be noted, however, is

'employed A brake is also here shown for tion by the spring 59 and said brake-band 80,` y

96 is held in firm engagement with lthe pulley 85, and will act to hold the motor-shaft at rest by the friction of the band. The

Normally, the movable part of the/ spring 59 is adjusted so that the movable j member of the fieldframe will not be attracted toward the stationary part on a less powerful overload than is designed and intended to start and operate the motor, but

`upon the occurrence of a suiiicient overload said movable part will be attracted toward the stationary part overcoming theforce. of

said-spring 59, and the brake will be moved to release its firm engagement with the pul- ,ley so that the motor is free to operate. The

operations of lifting the movable part of the field-frame and of starting the motor are, of course, practically simultaneous upon the occurrence of an overload which is at least as great as it is designed and intended shall "operate the motor. The brake is employed particularly in case the motor is arranged directly in the transformer circuit, the overload relay being omitted, as shown in Fig. 12, as in such case it prevents the motor from starting until influenced by a current sufficiently strong to overcome the force of the spring 59.

` The motor here shown, having the capability of causing the sWitch-operating-device or circuit-closing member to engage its rotary actuator, and also 'of rotating said actuator and switch-operating-device inengagement with it, is of advantage as an electro-responsive means adapted to be controlled by the overload and to in turn operate the switchoperating means, even though it does not possess the capabilities hence I lay claim thereto separately, but a. 4motor having all the capabilities is the Ipreferred embodiment of my invention.

Referring to Fig. 13,.a diagram is shown of a transformer, a transformer circuit and motor, the motor field being connected with `the circuit and operated `byv ay constant potent-ial, but the current in the armature varies according to the strength of the overload and the magnetic circuit and windings of the armature are so arranged that the speed of the armature varies up to the point of saturation where it attains its maximum speed, and for higher current values the speed does not increase. 4'llhis enables the results heretofore described to be attained.

Referring to Fig. 14 a diagram is shown of a transformer and transformer circuit having connected therein an overload relay and a motor arranged in a battery circuit which is controlled by the .overload relay through a variable resistance. lin this instance the speed of the motor varies according to the amount of resistance which is included and the amount of resistance is controlled by the solenoid 75 arranged in the series transformer circuit 70 until all of the resistance is cut out at approximately three times the full load of the circuit, and at this point the motor attains its maximum speed, and on higher current values will run at the same speed. y

Referring to Fig. 15, a modification similar to Fig. 14 is shown, wherein the overload relay controls theyfield windings of the motor instead of cutting resistances in and out.

lin said" Fig. 15 the motor represented is a repulsion motor instead of a direct current motor.

Referring to Figs. 16 and 17 a repulsion motor is shown in which the speed of the motor is dependent upon the position of the brushes on the commutator, and the brushes of the motor are arranged to be controlled by the overload relay, thus producing'the same effect, so far as the speed of the motor is concerned as is produced in Fig. 14.

Referring to Fig. 18 the motor is the same as represented in Fig. 17, the brushes of the motor .are short-circuit-ed but movable into did'erent positions according t-o the strength of the overload. in this instance normally the field coils are short-circuited and when said short-circuit is `opened the field c oils are cut in and the brushes are moved relatively to their cooperating member. The same results are herein attained as in Figs. 16 and 17.

l claim 1. A selective time-limit. controlling-device for electric-switches having an operating-device requiring a prolonged period of time to operate the switch, and means responsive to an overload current to actuate said operating-device, which means consumes varying periods of time in causing the operating-device to operate the switch according to the current value of the overload up to a `predetermined current value, and constant periods of time regardless of the current value of the Overload on over- Lomme loads of higher current values, substantially as described.

2. A selective time--limit controlling-device for elect-ric-switches having an operating-device requiring a prolonged period of time to operate the switch, and means responsive to an overload current to actuate said operating-devices, which means exerts a force proportionate to the current value of the overload up to a predetermined current value, and exerts a constant force regardless of the current value of the overload o-n loads of higher current values, substantially as described.

3. A selective time-limit controlling-device for electric-switches having an operating-device requiring a prolonged period of time to operate t-he switch, and means responsive to 4an overload current to actuate said operating-device at a variable speed according to the current value of the overload, up to a predetermined current value, and at a definite speed, regardless of the current value of the overload on overloads of higher current values, substantially as described.

4. A selective time-limit controlling-device for electric-switches, comprising switchoperating means requiring a prolonged period of time to operate the switch, and an electro-magnetic device responsive to an overload current to actuate said switchoperating means, said electro-magnetic device consuming periods of time of diit'erentlength in causing the switch-operating means to operate the switch according to the current value of the overload up to a predetermined current value, and periods of time of the same length on overload of higher current values, substantially as described.

5. A selective time-limit controlling-device for electric-switches comprising switchoperating means. requiring a prolonged period of time to operate the switch, and an electro-magnetic device responsive to an overload current to actuate said switch operating-means which exerts a force proportionate to the current value of an overload up to its point of saturation, and exerts its maximum force on overloads of higher current values, substantially as described.

6. A selective time-limit controlling-device for electric-switches comprising switchoperating means requiring a prolonged period of time to operate the switch, an v electro-magnetic device vresponsive to an overload current to actuate said switch operating-means at a variable speed according to the current value of the overload up to its point of saturation, where its maximum speed is attained, and at its maximum speed on overloads of higher current value, substantially as described.

' 10 overload up t'o the point of saturation, and

above said point is constant-regardless of the current value of the overload, substantially as described.

8. A selective' time-limit controlling-dey vice for electric-switches comprising operating-means for the switch, a movable element to control said operating-means, a coil for said movable element having its magnetic-circuit and windings-so proportioned that upon the occurrence of an overload which is less than approximately three times the full load of the circuitv which is controlled by the switch, the force exerted by the movable element is variable according to the strength of the overload, and upon the occurrence of a heavier overload the 'force exerted by the movable element. is constant regardless of the strength of the overload, subst-antially as described.

9. A selective time-limit controlling-device for electric-switches consisting of a self-restoring operating-device requiring a prolonged period of time to operate the switch, an electric-motor to actuate said operating-device, which is variably responsive to an overload current according to the value thereoi2 up to a. predetermined value, and is definitely responsive to overloads ot' higher current values, said operating-device 4@ being movable into'and out .of .coperative relation with its actuating-means by means controlled by the overload' current, resuming its normal position when the overload current ceases, substantially as described.

l0. A selective time-limit controlling-device for electric-switches consistin of acontroller tor the switch, an operating-device for said controller requiring a'prolonged period ci time to operate the controller, a 5o rotatable actuator into and out of engagement with which said operating-device is movable, an electric-motor responsive to an overload current to rotate said actuator at a variable speed according-tothe value ofi` the overload up to a predetermined value, yand lat a definite speedv in response to overloads of higher values, and lmeans responsive to an overload to move said operating-device into. engagement with its actuator, which permits of its return to normal when the overload ceases, substantially as described.

1l. In a selective time-limit devlce for electric-switches, the combination of a cir-' cuit-closing member, means for imparting a speed of movement forward to said-member upon the creation of an overload, which speed varies according to the current value of the overload up to a predetermined current value and remains constant on higher current values, and means to return said circuit-closing member to its original position when the overload falls below a predetermined current value, substantially as described.

l2. A time-limit controlling-device for electric-switches consisting of an operatingdevice requiring a prolonged period of time to operate the switch, an actuator therefor, an electric-motor for driving said actuator responsive to an overload current, and movable means supporting said operating-device, whereby said device is movable into and out of engagement with its actuator, said movable means being arranged in the magnetic-field of the motor and adapted to be moved by the attractive influence of said field, substantially as described.

13. A time-limit controlling-device for electric-switches consisting of an operatingdevice requiring a prolonged period of time lto operate the switch, an actuator therefor,

an electric-motor for driving said actuator responsive to an overload current, the fieldframe of said motor being composed of two parts, one of which is movable with relation to the other by the magnetic iniiuence due to the current traversing the field-coils, said movable part bearing the o p eratingdevice and permitting movement otP said device into and out of engagement with its actuator, substantially as described.

v 11i. A time-limit controlling-device for electric-switches consisting oiE a switch-controller, an operating-device requiring a prolonged -period of time to cause the switchcontroller to operate the switch, an actuator into and out oit engagement with which said operating-device is movable, an electricmotor for driving said actuator/which is responsive'to an overioad current, and movable means supporting said operating-device and permitting movement of said device t'oward and from its actuator; said means being arranged 1n the magnetic-field 'of the motor and adapted to be moved by 'the attractive influence of said iield, substantially' as described.

15. A time-limit controlling-device for y electric-switches, consisting of a switch-con-y troller, an operating-device for said controller requiring a prolonged period of time to cause said controller to operate the switch,`an actuator into and out of engagement with which said operating-device is movable, an electric-motor for driving said actuator whichis responsive to an overload current, the field-frame of said motor being composed of two parts,'one of which is movable with ,relation -to the other by the magnet-ic influence due to the current passmeans whereby it isl permitted to operate` only on `an overload of at least a given strength, substantially as described.

17. A time-limit controlling-device for electric-switches consisting of an operating device requiring a prolonged period of time to operate the switch, anvactuator therefor, an electric-motor for driving said actuator responsive to an overload current, and movable means supporting said operating-device, whereby said device is movable into and out of engagement with its actuator, said movable means being arranged in the magnetic-eld of the motor and adapted to be moved by the attractive influence ofy saidy held, and an adjusting-device for said m'ovable means whereby it is permitted to operate only on an overload of at least a given strength, substantially as described.

18. A time-limit controlling-device tor 2e]ectricswitches consisting of an operatingdevicevfor the switch, an actuator into and outfot engagement with which said operating-device is movable, an electric-motor for driving said actuator which is responsive to an overload current, means to move said operating-device into engagement with its actuator which is responsiveto an overload of at least a given strength'which permits return of said operating-device to normal y when the `overload ceases, substantially as described.

19. A time-limit controlling-device for electric-switches lconsisting of an operating device for the switch, an actuator into and out of engagement with which said operating-device`is movable, an electric-motor for maarre.

driving said actuator which is responsive to an overload current, means to move said operating-device into engagement with its actuator which is responsive'to an overload current: which permits return of said means to normal when the overload ceases, and an adjusting-device for said means which permits it to operate only upon an overload of at least a given strength, substantially as described.

20. A time-limit controlling-device for electric-switches consisting of an operatingdevice for the switch, an actuator therefor, an electric-motor for driving said actuator which is responsive to an overload current, movable means supporting said' operatingdevice whereby said device is movable into and out of engagement with its actuator, said movable means being arranged in the magnetic-field of the motor and adapted to be moved by the attractive influence of said ield, a brake for holdingpthe motor at rest, and means to move said brake to release the motor which is connected with said movable means, substantially as described.

21. A. time-limit controlling-device for electric-switches consisting of an operatingdevice for the switch, an actuator therefor, an electricmotor for driving said actuator which is responsive to an overload current, movable means supporting said operatingdevice whereby said device is movable into and out of engagement with its actuator, said movable means being arranged in the magnetic iield of the motor and adapted to be moved by the vattractive influence of said held, an adjusting-device for said movable means whereby it is permitted to operate only on an overload of at least a given strength, a brake for holding the motor at rest, and means to move said brake to release the motor, which is conected with said movable means, substantially as described. ,A

ln testimony whereof, l have signed my name to this speciication, in the presence of two subscribing witnesses.

GEURGE A. BURNHAM. 

